A Questionstorm is a meeting format where attendees are only allowed to ask questions. The goal is to explore the edges of a poorly defined problem space. Performing a series with the stakeholders who are most important to the outcomes of your problem. Learn what concerns are top of mind for these groups, which in turn can help direct your future requirements gathering. post 
Questorming takes a somewhat different approach. Its aim is not so much to get a group to come up with "solutions" to a "problem" as to come up with well-stated and well-selected questions or problem formulations. In one sense it addresses the process leading up to what is done in more conventional brainstorming: formulating the problem to be solved by the group. In another sense it is brainstorming in which the problem for the group is to find the answer to the metaquestion, "What are the best questions we need to ask right now?". archive
See also Event Storming